Results 1 to 6 of 6

Thread: MCS2000 RX Sensitivity

  1. #1
    Join Date
    Sep 04, 2015
    Location
    In the Corn
    Posts
    252
    Thanks
    86
    Thanked 188 Times in 74 Posts
    Country: United States

    Default MCS2000 RX Sensitivity

    Apologies for the frequent posting recently, but I've had time to take a lot of radios to the bench for tune ups recently and have been having strange issues popping up. I posted this one over on BB but I figure some folks on here could lend a hand as well.

    I've been working on my base station, a HP VHF MCS2000. Over the past month or so, I noticed a few fringe repeaters started to sound much weaker than usual. After testing my antenna system to make sure everything was A-OK, I narrowed it down to the radio itself. First things first was to get the REFOSC in spec, but that didn't solve the issue. I also played with the bandpass filters without improvement as well.

    I've actually found two interesting issues through my testing this morning:

    1) In MCS2000 tuner, on the 146.0625 test freq, I can get 12dB SINAD at around -102dBm which is not great. With the radio in normal operation, on the same frequency, it takes until -85dBm to get 12dB, which is horrendous. So, there's obviously something changing between test mode and normal mode.

    2) When closing out of tuner, just before the radio reboots, for a brief moment the test signal I'm feeding in becomes crystal clear through the radio speaker where before it was marginal and noisey. While I can't seem to figure out why, this leads me to believe these sensitivity problems are a software issue and not a hardware issue.

    So I'm curious if anyone has seen either of these issues before, and how I can fix them if at all. I'm going to be doing some more testing up here today when I have the time, but for now I've got to get going.


  2. #2
    Join Date
    Dec 21, 2011
    Posts
    4,065
    Thanks
    2,992
    Thanked 5,830 Times in 1,716 Posts
    Country: Canada

    Default

    What firmware version are you working with?

    Narrowband or wideband channels?

    Also, likely unrelated as per your description, there's a "normal" and "high sensitivity" RXFE configuration, per board/parts layout, etc. I never did get around to that project as the radios I was supposed to receive, WERE NEVER SHIPPED (cough cough, certain moderator... hahah)

    Hope to see this issue resolved.

  3. #3
    Join Date
    Sep 04, 2015
    Location
    In the Corn
    Posts
    252
    Thanks
    86
    Thanked 188 Times in 74 Posts
    Country: United States

    Default

    Firmware is R5.14ish (going off of memory). Radio was working fine for several months so I doubt that’s the issue.

    The problem happens on both wide and narrow channels. NB seems to be slightly more sensitive, but at mostly only a few dB more.

    The symptoms of sudden loss of sensitivity seems to indicate a hardware fault, but at the same time the fact that it gets much better when exiting tuner seems to imply a software issue. Confusing for sure.

    I’ve got a second VHF 2000 that I replaced the problem one with. At least for now it seems to be doing better. This issue coupled with a high RFI environment at home makes it hard to tell how well the radio actually does with fringe repeaters.

  4. The Following User Says Thank You to axel For This Useful Post:

    Mars (Mar 28, 2018)

  5. #4
    Join Date
    May 27, 2012
    Posts
    89
    Thanks
    1
    Thanked 60 Times in 31 Posts

    Default

    This may sound completely ridiculous, but, open the radio and snug all the torx screws down holding the board to the chassis.

    I've actually had several where this was the solution to the issue...

  6. The Following 8 Users Say Thank You to phantom For This Useful Post:

    AD0JA (Apr 07, 2018),Alpha (Mar 28, 2018),axel (Mar 28, 2018),b16a2 (Mar 29, 2018),Mars (Mar 28, 2018),p47r4ck (Apr 01, 2018),radiotinkerer1 (Mar 29, 2018),triptolemus (Mar 28, 2018)

  7. #5
    Join Date
    Sep 04, 2015
    Location
    In the Corn
    Posts
    252
    Thanks
    86
    Thanked 188 Times in 74 Posts
    Country: United States

    Default

    I’ll try that out. I can imagine ground/shielding could be an issue if something was loose.

    I also threw the “good” MCS on the analyzer and got 12dB SINAD at -114dBm which is quite a bit more in line with official spec. (Still not perfect - but I’ll take it)

  8. #6
    Join Date
    Sep 04, 2015
    Location
    In the Corn
    Posts
    252
    Thanks
    86
    Thanked 188 Times in 74 Posts
    Country: United States

    Default

    Update: it worked! Cracked 'er open and tightened all the board screws. Buttoned it back up and fired up the R&S.

    You have no idea how frustrated I am that such a stupid solution actually worked. The thing is perfect now, 12dB SINAD at -123dBm. That's getting close to APX sensitivity.

    Kudos to you sir. I'll have to do that to my other MCS too and see if it makes it any better.

  9. The Following 7 Users Say Thank You to axel For This Useful Post:

    AD0JA (Apr 07, 2018),Alpha (Mar 28, 2018),b16a2 (Mar 29, 2018),crazyboy (Mar 28, 2018),Mars (Mar 28, 2018),motorola_otaku (Apr 02, 2018),radio (Mar 28, 2018)